Palladium-catalysed [π2a+π2s] cycloadditions of α-bromoalkyl ketenes to cyclopentadiene

7-Substituted bicyclo[3.2.0]hept-2-en-6-one derivatives were identified as intermediates towards biologically interesting compounds. An improved synthesis of 7-alkyl-7-bromobicyclo[3.2.0]hept-2-en-6-ones by palladium-catalysed [π2a+π2s] cycloaddition of α-bromoalkyl ketenes to cyclopentadiene is described. Increased yields and increasing exo alkyl cycloadducts were observed with various palladium catalysts under standard dehydrochlorination conditions.